1. Field of Invention
The present device relates generally to optical apparatus for gathering imagery. More specifically, the device relates to a forward looking infrared (FLIR) apparatus having multiple optical systems.
2. Background Information
Forward looking infrared (FLIR) imaging systems are known. Such systems can be used with laser designators that illuminate the target with a laser beam to enhance tracking, such as noted in U.S. Pat. No. 4,155,096, the disclosure of which is hereby incorporated by reference in its entirety. Moreover, FLIR imaging systems can employ a laser and an associated detection scheme for illuminating and detecting a particular “hit spot” on a certain area of a target to enhance the likelihood of a target kill, such as noted in U.S. Pat. Nos. 5,900,620 and 5,918,305, the disclosures of which are hereby incorporated by reference in their entirety. Typically, FLIR imaging systems on military aircraft include optics to provide a wide field of view (WFOV) for piloting and optics to provide a narrow field of view (NFOV), for targeting, such as described in U.S. Pat. Nos. 5,418,364, 5,005,083, 5,049,740, 5,933,272, and 5,936,771, the disclosures of which are hereby incorporated by reference in their entirety.
Generally, the FLIR system and the laser designator are separate modules because FLIR optics typically will not transmit the wavelength of the laser designator or because the FLIR detector will not respond to the wavelength of the laser designator. In such systems, the FLIR system and the laser designator system must be boresighted to insure that the laser designator accurately illuminates the target. Boresighting is typically accomplished using an optical device (a boresight tool) that bridges the apertures of the FLIR system and laser designator system such that some of the emission from the laser designator is converted to thermal energy that can be imaged by the FLIR system for aligning the two systems.
However, the relative alignment (lines of sight) for FLIR and laser-designator systems designed as separate modules will typically change due to vibration, temperature changes, and other environmental conditions. Accordingly, repeated boresighting in such systems is necessary. Whether such boresighting is accomplished manually or automatically, such as described in U.S. Pat. No. 4,155,096 to Thomas et al., the boresighting tool adds to the complexity, weight, and cost of the overall FLIR/laser-designator system.
U.S. Pat. No. 5,900,620 discloses optics that both receive radiation from a target and receive a reflected laser beam incident on the target. The system described therein partially shares certain optical components along a partial common optical axis. However, the system therein also includes separate optical components disposed along different optical axes for changing polarization and for directing the target radiation and the reflected laser radiation to separate detectors. Accordingly, the system disclosed in U.S. Pat. No. 5,900,620 has the potential to suffer from the alignment problems requiring corrective boresighting similar to those noted above. Moreover, the system therein utilizes separate detectors for the above-noted functions, thereby having higher power requirements and additional complexity compared to a system utilizing a single detector for the above-noted functions.